High frequency coil



Marcb 4, 1941. RUST 2,233,748

HIGH FREQUENCY COIL Original Filed April 24, 1938 2 Sheets-Sheet 1 II III! INV EN TOR.

' v '05 MEYER RUST BY )k% W ATTORNEY.

March 4, 1941. ug-r 2,233,748

HIGH FREQUENCY COIL Original Filed April 24, 1936 2 Sheets-Sheet 2 I INVETOR. NOEL MEYER RUST ATTORNEY.

Patented Mar. 4, 1941 UNITED STATES HIGH FREQUENCY COIL Noel Meyer Rust, Chelmsford, England, assignor to Radio Corpmation of America, a corporation of Delaware Original application April 24, 1936, Serial No. 76,122. Divided and this application January 12, 1938, Serial No. 184,545.

May 11, 1935 3 Claims.

This invention relates to coil constructions for use in electrical high frequency circuits and to circuit arrangements incorporating the same.

This application is a division of my copending application Serial No. 76,122, filed April 24, 1936, and is particularly directed to the use of an improved coil in a high frequency circuit.

An important object of the invention is to provide quarter wave and half wave length coil constructions which shall be very cheap, light, and of low losses and which can be made directly self-supporting, i. e. without needing terminals or mountings. Where terminals or mountings are provided, they are arranged to be out of the field of the coil.

According to this invention, a coil structure for use as a resonant device'in high frequency electrical circuit arrangements comprises an inner conductive coil winding positioned within an outer conductive screen member and is characterized in that said winding and screen member are so constructed and supported that there is no solid dielectric material between the face of said winding presented to said screen member and said screen member.

The invention is illustrated in the accompanying drawings, in which:

Fig. 1 is a longitudinal sectional view showing one embodiment of the coil construction of this invention;

Fig. 2 is a cross section of Fig. 1;

Fig. 3 is a side elevation, partly in section, of another coil construction of this invention;

Fig. 4 is an end elevation of Fig. 3;

Fig. 5 is a developed view showing part of a screen conductor;

Fig. 6 is a perspective View of a screen structure;

Fig. '7 is an end view of Fig. 6;

Fig. 8 illustrates an oscillator circuit employing the coil construction of this invention;

Fig. 8a is another oscillator circuit employing the coil construction of this invention;

Fig. 9 is a modified oscillator circuit using a coil construction of this invention;

Fig. 10 shows a circuit diagram for employing coils constructed according to this invention;

Fig. 11 is another circuit diagram employing coils constructed according to this invention; and

Fig, 12 is a circuit diagram which is suitable for the reception of modulated signals using coils of this invention.

Referring to Figs. 1 and 2 which are mutually perpendicular sectional views showing one form In Great Britain of construction in accordance with the invention, a quarter or half wave length coil construction comprises a helix I of solid conductive wire or strip e. g. copper, concentrically arranged within a split cylindrical member 2 of conductive material, e. g. copper foil. The helix is wound over parallel insulating support rods 3 which carry at or near their ends further radial insulating rods 4 which in turn carry additional insulating rods 5 running parallel to the axis of the helix and also parallel to the rods 3 over which the said helix is wound. The outer insulating rods 5 serve to support the split foil cylinder 2 which is positioned within the said outer rods 5 and may be secured or otherwise aiiixed thereto in any convenient manner. Since in this arrangement the supporting rods 3 for the helix are inside the turns thereof and the supporting rods 5 for the foil are outside the same, the insulating material of which those rods are constituted will substantially not be within the field between the helix and foil, and accordingly dielectric losses will to a great extent be reduced. It will be appreciated that the middle point of the helix of a half wave coil construction in accordance wtih the preceding description will be a potential node and accordingly it may be directly connected to the split cylinder of foil.

Another construction of coil structure in accordance with this invention is shown in Figs. 3, 4 and 5. In these figures, Fig. 3 is an elevation with part of the screen portion broken away to show the construction; Fig. 4 is an end view, and Fig. 5 is a developed view of part of the screen conductor.

Referring to Figs. 3 to 5, the inner conductor of the line is in the form of a helix l of fiat strip conductor wound upon and stuck to an inner approximately cylindrical former 6 of paper or the like impregnated and coated with a suitable insulating varnish. The former 6 is somewhat longer than the helix and extends beyond it at both ends. The screen conductor 2 is of copper foil and is stuck to the inside of an approximately cylindrical backing 1 also of paper impregnated with a suitable varnish. The screen conductor is split with a plurality of splits 8 running parallel to the axis of the Whole structure, adjacent splits starting from opposite edges and extending rather less than the length of the screen. The said screen conductor is made by slitting a sheet of copper foil as shown in Fig. 5 and then bending it up into a cylinder, the edges, which are at right angles to the slits, forming the circular edges of the bentup cylinder. The conductor 2 with its outer backing 'I is pushed over the inner conductor I and former 6 and is held in place by strips 9 of fairly stiif insulation impregnated or coated paper. The ends of the conductor I are brought out parallel to the axis and are held firmly by insulation coated or impregnated paper layers III which pass over the conductor I and also over the strips 9 and are stuck in position.

Figs. 6 and '7 are respectively a perspective view and an end view of a screen structure which may be substituted for that adopted in the coil structure shown in Figs. 3 to 5. In Figs. 6 and '7, the screen is in the form of a number of copper foil strips 2a stuck to the inside of an insulation impregnated or coated cylindrical backing I. The copper strips may be earthed as shown in Fig, 6 by wires Illa leading out to a common point, or, instead of using wires the strips themselves may be extended beyond the backing and brought out to a common point in the same way as the wires "la 01 Fig. 6.

It will be observed that in all the illustrated coil structures the inner conductor is above its insulating support, the face of said conductor presented to the screen being free of insulating material and the outer conductor is inside its insulating support. Thus, the field between outer and inner conductors does not pass through any insulating material (other than air)-an important point for securing high efliciency in high frequency operation.

There are many circuit arrangements in which coil constructions as just described may be employed with advantage. For example, as shown in Fig. 8, a thermionic valve oscillator may comprise a triode I I whose grid I2 is connected to its cathode I3 through a condenser shunted grid resistance combination HI, I5, and Whose anode I6 is connected to one end of the coil proper (the inner conductor I) of a half wave coil construction as just described, the other end of the coil proper being connected through a condenser IT to the grid of the valve. The midpoint I8 of the coil I is connected to the outer conductor of the coil construction (the split cylindrical foil 2) and is earthed through a condenser I9 and connected through an anode battery 29 to the valve cathode, which is also earthed. Fig. 8a shows what is in some respects a preferable variant of the circuit of Fig. 8. In Fig. 8a, automatic bias is provided by the capacity shunted resistance combination in the cathode lead. As like references are used in Figs. 8 and 8a for like parts, it is thought unnecessary further to describe Fig. 8a.

In a modified oscillator arrangement in accordance with this invention and shown in Fig. 9, one end of the coil I of a half wave coil construction as above described is connected through a capacity shunted grid resistance combination I4 I5 to the grid I2 of a triode II and the other end is connected through a condenser II to the anode IS, the midpoint I8 of the coil I being connected to the outer conductor 2 and to the cathode I3 directly, anode potential being applied to the anode through a choke 2I.

In another arrangement a half wave coil construction as above described is employed as illustrated in Fig. 10 in the anode feed circuit of a thermionic amplifier. The anode 22 of the amplifier valve 23 is connected to one end of the coil I and the other end of said coil proper is connected through a condenser 24 to the control grid 25 of a succeeding amplifier valve 25. The midpoint I8 of the coil I is connected to the outer conductor 2 and through an anode potential source (not shown) to the cathode of the valve 23.

In a modification (also illustrated in Fig. 10) of the last described arrangement, a half wave coil construction is employed in the grid feed circuit. In Fig. 10, this use of a half wave coil construction is illustrated as adopted for the valve 21 the coil I being connected at one end through a condenser 23 to the anode of the amplifier valve 26 and the other end of the coil I being connected to the grid 29 of the succeeding valve 21. Anode potential is applied to the anode of valve 26 through a choke 30 and the center I3 of the coil I is connected to the outer conductor 2 (the foil) and to the cathode point directly.

In yet another arrangement illustrated in Fig. 11 and suitable for use where low impedance valves are required to be employed, a source of high frequency energy, e. g. an aerial 3|, is connected to one end of the coil I of a half wave coil construction, as above described, the other end of said coil I being connected to the grid 32 of a low impedance valve 33. The cathode 34 of the said valve is connected through a capacity shunted grid resistance combination 35, 36, to the cathode point to which is also connected the outer conductor 2 and a point I8 to one side of the electrical center of the coil I. The point I8 is selected so as to obtain presentation of the required impedance at the ends of the coil, the high impedance end being, of course, that which faces toward the grid. If desired, a tuning condenser 31 may be shunted between one end of the coil I and the outer conductor 2. The anode 33 or the low impedance valve is connected to one end of the coil I of a second half wave coil construction, the other end of the said coil I being capacity coupled as shown to the grid of a succeeding valve 39 and a point I8 to one side of the center of said coil being connected to its associated outer conductor 2 which in turn is connected through a source of anode potential (not shown) to. the cathode point. Again, a tuning condenser 43 may, if desired, be shunted between the anode of the first valve 33 and the outer conductor 2' of the second half wave coil construction.

It should be noted that where for tuning or other purposes variable condensers are employed, these condensers should be kept as small as possible; in fact, where circumstances permit, it is preferred to omit condensers altogether.

In another circuit arrangement in accordance with this invention and illustrated in Fig l2- this arrangement is very suitable for reception of television modulated signals and for other purposes where a very wide band of frequencies is to be dealt with-incoming signals, which may be received, for example, upon a receiving dipole 41] are fed in via crossed leads 42 and are applied between two points 43, 44 symmetrically disposed upon either side of the center point !8 cf the coil 1 of a half wave coil construction in accord-- ance with this invention, this center point It being connected to the outer conductor 2 and also to the common cathode point 45 of two push-pull connected high frequency valves ll. The grids of these valves 48, 41 are connected respectively each to one end of the coil I and the anodes of the said valves are connected each to one end of the coil I" or a second half wave coil construction I" 2". The electrical center IQ of the coil of the second half wave coil construction is connected to the outer conductor 2 thereof and, througha source (not shown) of anode potential, to the common cathode point 45. Each anode is capacity coupled to one or the other grids of two further triodes 43, 49, also in push-pull, the grids of these further valves being connected to one another through the coil I" of a third half Wave coil construction I" 2" in accordance with this invention, the midpoint l8 of the coil of the said third construction being connected to the outer conductor 2 thereof and to the cathode point of the second pair of pushpull valves 48, 49. The second and third half Wave coil constructions, together with the two coupling condensers, may be arranged to constitute a bandpass filter and owing to the high eiiiciency and small losses of the arrangement described a very satisfactory bandpass filter arrangement can be obtained even when short wave radio energyfor example, energy of a Wave length of seven metersmodulated with a range of signals corresponding to modern high definition television signals-e. g. ranging from twenty-five cycles to two megacycles or more.is in question. 563 represents a screen.

What is claimed is:

l. A high frequency electrical coil and circuit arrangement comprising a helical coil Whose electrical length is one-half a wave length, said coil being concentrically arranged within a split cylindrical member of conductive material, a tap on said helical coil and connected to said split cylindrical member, said tap being located to one side of the electrical center of said coil to obtain presentation of the required impedance at the ends of the coil, an input and an output circuit, said output circuit including a thermionic tube comprising at least an anode, grid, and cathode, at least one end of said coil being connected to the anode of said tube, the other end of said coil being connected to said input circuit, the cylindrical member of said coil being connected to the cathode of said tube.

2. A high frequency electrical coil and circuit arrangement comprising a first and a second helical coil whose electrical wave lengths are one-half Wave length, each one of said coils being concentrically arranged within a split cylindrical member of conductive material, a tap on each one of said helical coils and connected to said split cylindrical member, said tap being located to one side of the electrical center of each one of said coils to obtain presentation of the required impedance at the ends of the coils, a first and a second thermionic tube each having at least an anode, grid and cathode circuit, one end of said first coil being connected to the grid circuit of said first thermionic tube, a source of high frequency energy connected to another end of said first coil, one end of said second coil being capacitively coupled to the grid circuit of said second thermionic tube, the other end of said second coil being connected to the anode circuit of said first thermionic tube, the cylindrical member of said first coil being connected to the cathode circuit of said first tube, the cylindrical member of the second coil being connected to the anode circuit of said second thermionic tube. 3.'A high frequency electrical coil and circuit arrangement comprising a first and a second helical coil whose electrical lengths are one-half wave length, each one of the coils being concentrically arranged within a split cylindrical member of conductive material, a tap on each one of said helical coils and connected to said cylindrical member, said tap being located to one side of the electrical center of said coil to obtain presentation of the required impedance at the ends of the coils, a first and a second thermionic tube each having at least an anode, grid and cathode circuit, a source of high frequency energy connected to one end of said first coil, the other end of said first coil being connected to the grid circuit of the first thermionic tube, the anode circuit of said first thermionic tube being connected to an end of said second helical coil, the other end of said last mentioned coil being capacitively coupled to the grid circuit of said second thermionic tube, the cylindrical member of the first one of said coils being connected to the cathode circuit of the first thermionic tube, the cylindrical member of the second coil being connected to the anode circuit of the second thermionic tube.

NOEL MEYER RUST. 

